AMD's chiplet-based design means they have plenty of other ways to make good use of parts that cannot hit the highest clock speeds. They have very little reason to do a 16-core low-clock part for their consumer desktop platform.

And your concerns about "a software limit that may or may not work" are completely at odds with how their power management works.

It isn't a "software limit" beyond just being controlled by writing to certain CPU registers via software. It's very much a feature of the hardware, the same feature that allows for overclocking the chips.

That's not how binning works. Quality silicon is also the ones that are more efficient. A flagship 65W part would be just as expensive as a result, it's the same-ish quality of parts.